In humans, the heart beats to sustain life. In normal operation, it pumps blood through the various parts of the body. More particularly, the various chamber of the heart contract and expand in a periodic and coordinated fashion, which causes the blood to be pumped regularly. More specifically, the right atrium sends deoxygenated blood into the right ventricle. The right ventricle pumps the blood to the lungs, where it becomes oxygenated, and from where it returns to the left atrium. The left atrium pumps the oxygenated blood to the left ventricle. The left ventricle, then, expels the blood, forcing it to circulate to the various parts of the body and from where it returns to the right atrium to start the oxygenation-deoxygenation cycle of the blood all over again.
The heart chambers pump because of the heart's electrical control system. More particularly, the sinoatrial (SA) node generates an electrical impulse, which generates further electrical signals. These further signals cause the above-described contractions of the various chambers in the heart to occur in the correct sequence. The electrical pattern created by the sinoatrial (SA) node is called a sinus rhythm.
Sometimes, however, the electrical control system of the heart malfunctions, which can cause the heart to beat irregularly, or not at all. The cardiac rhythm is then generally called an arrhythmia. Arrhythmias may be caused by electrical activity from locations in the heart other than the SA node. Some types of arrhythmia may result in inadequate blood flow, thus reducing the amount of blood pumped to the various parts of the body. Some arrhythmias may even result in a Sudden Cardiac Arrest (SCA). In an SCA, the heart fails to pump blood effectively, and, if not corrected, can result in death. It is estimated that SCA results in more than 250,000 deaths per year in the United States alone. Further, an SCA may result from a condition other than an arrhythmia.
One type of arrhythmia associated with SCA is known as Ventricular Fibrillation (VF). VF is a type of malfunction where the ventricles make rapid, uncoordinated movements, instead of the normal contractions. When that happens, the heart does not pump enough blood to deliver enough oxygen to the vital organs. The person's condition will deteriorate rapidly and, if not corrected in time, will result in death, e.g. within ten minutes.
Ventricular Fibrillation can often be reversed using a life-saving device called a defibrillator. A defibrillator, if applied properly, can administer an electrical shock to the heart. The shock may terminate the VF, thus giving the heart the opportunity to resume normal contractions in pumping blood. If VF is not terminated, the shock may be repeated, often at escalating energies.
A challenge with defibrillation is that the electrical shock must be administered very soon after the onset of VF. There is not much time to do this since the survival rate of persons suffering from VF decreases by about 10% for each minute the administration of a defibrillation shock is delayed. After about 10 minutes the rate of survival for SCA victims averages less than 2%.
The challenge of defibrillating early after the onset of VF is being met in a number of ways. First, for some people who are considered to be at a higher risk of VF or other heart arrythmias, an Implantable Cardioverter Defibrillator (ICD) can be implanted surgically. An ICD can monitor the person's heart, and administer an electrical shock as needed. As such, an ICD reduces the need to have the higher-risk person be monitored constantly by medical personnel.
Regardless, VF can occur unpredictably, even to a person who is not considered at risk. As such, VF can be experienced by many people who lack the benefit of ICD therapy. When VF occurs to a person who does not have an ICD, they collapse, because the blood flow has stopped. They should receive therapy quickly after the onset of VF or they will die.
For a VF victim without an ICD, a different type of defibrillator can be used, which is called an external defibrillator. External defibrillators have been made portable, so they can be brought to a potential VF victim quickly enough to revive them.
During VF, the person's condition deteriorates because the blood is not flowing to the brain, heart, lungs, and other organs. The blood flow must be restored, if resuscitation attempts are to be successful.
Cardiopulmonary Resuscitation (CPR) is one method of forcing blood to again flow in a person experiencing cardiac arrest. In addition, CPR is the primary recommended treatment for some patients with some kinds of non-VF cardiac arrest, such as asystole and pulseless electrical activity (PEA). CPR is a combination of techniques that include chest compressions to force blood circulation, and rescue breathing to force respiration.
Properly administered CPR provides oxygenated blood to critical organs of a person in cardiac arrest, thereby minimizing the deterioration that would otherwise occur. As such, CPR can be beneficial for persons experiencing VF, because it slows down the deterioration that would otherwise occur while a defibrillator is being retrieved. For patients with an extended down-time, survival rates are higher if CPR is administered prior to defibrillation.
One common challenge for both automated and manual rhythm assessment in connection with defibrillation is to accurately triage patients with chest pain or other symptoms suggestive of a possible acute coronary syndrome (ACS, i.e., acute myocardial ischemia or infarction [AMI]). Although there are many ways of classifying a patient based on ECG waveforms, one particularly effective way is by use of a set of data within the ECG waveform known as an ST-segment. Using the ST-segment of an ECG waveform that may typically be taken from a standard 12-lead ECG, a possible ACS patient may be classified into one of three groups:                1. STEMI (ST elevation myocardial ischemia/infarction)        2. High-risk UA/NSTEMI (unstable angina/non-ST-elevation myocardial ischemia/infarction)        3. Other (either low/intermediate risk UA/NSTEMI, or non-ACS)        The classification of a patient based on ST-segment or other data from an ECG waveform can affect the patient's destination (e.g., catheterization laboratory [cath lab]) and treatment (e.g., prehospital drug therapy).        
Accurate triage of possible ACS patients from the 12-lead ECG is a challenge for expert cardiologists and a greater challenge for less-experienced clinicians (e.g., new cardiologists, new emergency physicians, and paramedics). Interpreting the 12-lead ECG for possible ACS patients is challenging for two general reasons. First, there are many patterns of abnormal ST levels that can occur, depending on the patient's coronary anatomy and on where the clot is located in the coronary tree. Second, there are many non-ACS conditions that can cause abnormal ST levels (e.g., left ventricular hypertrophy) or other data readings on an ECG waveform. In addition, automated 12-lead programs cannot achieve the accuracy of expert cardiologists because the triage decision often depends on patient symptoms (e.g., “It feels like an elephant is stepping on my chest”), clinical history (e.g., prior myocardial infarction), and presentation (e.g., chest trauma from a seat belt due to a motor vehicle collision).
Incorrect triage can have substantial consequences. For example, missing a STEMI can result in a large myocardial infarction or even death in a patient whose myocardium could have been salvaged with timely treatment in the cath lab. A false STEMI alert can needlessly bring the cath lab to the hospital in the middle of the night. Missing or mis-reading other data in the waveform of an ECG may also lead to false diagnosis and improper treatment.
While advanced medical device solutions exist for interpreting data in a 12-lead ECG waveform, defibrillator operators may benefit from the display of 12-lead ECG waveforms that are more informative, intuitive and user friendly.